Preliminary studies in these laboratories have resulted in the discovery of a novel hydrogen peroxide mediated ring expansion that is suitable for the synthesis of medium to large ring compounds. This rearrangement involves the solvolysis of homoallylic brosylates in conc. H202 and results in a two-carbon ring expansion producing hydroxy-ketone derivatives in excellent yields. The reaction apparently involves initial solvolysis to the cyclopropylcarbinyl-cyclobutyl carbocation followed by Criegee-type migration of the cyclobutyl isomer. This proposal deals with the basic studies to exploit this novel reaction. Of primary interest are investigation of systems that will enable the determination of functional group compatibilities and stereochemical interactions during the rearrangement. The rearrangement has the potential of providing a unique type of cross-ring stereochemical control in the synthesis of medium-ring compounds.